Switching schemes for multiple antennas

ABSTRACT

Signals from multiple antennas are evaluated in a wireless device having one receiver chain and the antenna receiving the highest quality signals is selected. The signal quality from the multiple antennas may be evaluated using the short symbols in the preamble or the beacon signals and the antennas dynamically selected to improve the performance of the wireless communications device.

Today's portable communication products such as cellular telephones andlaptop computers require reception of an accurate data stream foreffective operation. The signal received by two antennas on a NetworkInterface Card (NIC) may be sequentially evaluated, with the antennasupplying the best signal quality selected to further receive data.Thus, the NIC may be used to evaluate signals received through twoantennas and based on the evaluation, lock onto the signal with the bestquality. This capability of selection is referred to as “switcheddiversity” and provides signal gain over a product that does not providesignal quality selection in combating signal fading.

It would be advantageous to have an improved method and circuit forevaluating signals from multiple antennas and selecting the signal withthe desired signal qualities.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 illustrates a wireless communications device having features forevaluating and selecting signals received from multiple antennas inaccordance with the present invention;

FIG. 2 illustrates a scheme for dynamically tracking the channelvariation that affects the signals received by the multiple antennas;

FIG. 3 illustrates the evaluation process for selecting antennas thatprovide the wireless communications device with the highest performance;

FIG. 4 illustrates another embodiment that dynamically tracks channelvariations that may affect the signals received by the multipleantennas;

FIG. 5 illustrates yet another embodiment that dynamically trackschannel variations that may affect the signals received by the multipleantennas; and

FIG. 6 illustrates a procedure for initiating coverage or booting up thewireless communications device.

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the figures have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements for clarity.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentinvention.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.Rather, in particular embodiments, “connected” may be used to indicatethat two or more elements are in direct physical or electrical contactwith each other. “Coupled” may mean that two or more elements are indirect physical or electrical contact. However, “coupled” may also meanthat two or more elements are not in direct contact with each other, butyet still co-operate or interact with each other.

Embodiments of the present invention may be used in a variety ofapplications, with the claimed subject matter incorporated intomicrocontrollers, general-purpose microprocessors, Digital SignalProcessors (DSPs), Reduced Instruction-Set Computing (RISC), ComplexInstruction-Set Computing (CISC), among other electronic components. Inparticular, the present invention may be used in laptop computers, smartphones, communicators and Personal Digital Assistants (PDAs), medical orbiotech equipment, automotive safety and protective equipment, andautomotive infotainment products. However, it should be understood thatthe scope of the present invention is not limited to these examples.

FIG. 1 illustrates a wireless communications device 10 having featuresfor evaluating and selecting signals received from multiple antennas inaccordance with the present invention. In this device the transceiverreceives and transmits modulated signals from four sectored antennas 14,16, 18 and 20, although the number of antenna is not a limitation of thepresent invention. The receiver chain may include amplifiers such as,for example, Low Noise Amplifiers (LNAs) and Variable Gain Amplifiers(VGAs) to amplify signals received from the selected antenna. Then, amixer circuit receives the modulated signals and down-converts thecarrier frequency of the modulated signals. The down-converted signalsmay then be filtered and converted to a digital representation byAnalog-To-Digital Converters (ADCs).

A baseband processor 24 may be connected to the ADC to provide, ingeneral, the digital processing of the received data withincommunications device 10. Baseband processor 24 may process thedigitized quadrature signals, i.e., the in-phase “I” signal and thequadrature “Q” signal from the receiver chain. On the transmitter side,transmitter 22 may receive digital data processed by baseband processor24 and use the Digital-to-Analog Converter (DAC) to convert the digitaldata to analog signals for transmission from multiple antennas 14, 16,18 and 20. Note that receiver 12 and/or transmitter 22 may be embeddedwith baseband processor 24 as a mixed-mode integrated circuit, oralternatively, the transceiver may be a stand-alone Radio Frequency (RF)integrated circuit.

An applications processor 28 may be connected to baseband processor 24through a signaling interface 30 that allows data to be transferredbetween baseband processor 24 and applications processor 28. A memorydevice 26 may be connected to baseband processor 24 and applicationsprocessor 28 to store data and/or instructions. In some embodiments,memory device 26 may be a volatile memory such as, for example, a StaticRandom Access Memory (SRAM), a Dynamic Random Access Memory (DRAM) or aSynchronous Dynamic Random Access Memory (SDRAM), although the scope ofthe claimed subject matter is not limited in this respect. In alternateembodiments, the memory devices may be nonvolatile memories such as, forexample, an Electrically Programmable Read-Only Memory (EPROM), anElectrically Erasable and Programmable Read Only Memory (EEPROM), aflash memory (NAND or NOR type, including multiple bits per cell), aFerroelectric Random Access Memory (FRAM), a Polymer FerroelectricRandom Access Memory (PFRAM), a Magnetic Random Access Memory (MRAM), anOvonics Unified Memory (OUM), a disk memory such as, for example, anelectromechanical hard disk, an optical disk, a magnetic disk, or anyother device capable of storing instructions and/or data. However, itshould be understood that the scope of the present invention is notlimited to these examples.

A channel evaluation circuit 34 evaluates the signal qualities of thesignals received by the multiple antennas and processed in the receiverchain and sets priorities to select the signals having the best quality.Although channel evaluation circuit 34 is shown in FIG. 1 as receiving adigital input, it should be noted that an analog signal from thereceiver chain may alternatively be used without changing the scope ofthe invention. A switch controller 32 receives the selection criteriafrom the channel evaluation circuit 34 and controls a switch 36 to lockonto the antenna that provides the best signal quality. The evaluationand selection scheme dynamically improves the performance of wirelesscommunications device 10.

FIG. 2 illustrates a scheme for dynamically tracking the channelvariation that affects the signals received by the multiple antennas inreceiver 12. For simplicity of illustration and by way of example,signals from the four antennas A₀, A₁, A₂ and A₃ may be evaluated, butit should be pointed out that features of the present invention allowsignals from any number of antennas to be evaluated.

To initiate a high-speed wireless Internet connection, laptop computersor other portable devices with Wi-Fi cards (or wireless fidelity) maytap into wireless Access Points (APs) which may be physically connectedto high-speed networks. The AP may then transmit frames between networkpoints as a unit complete with the addressing and protocol controlinformation.

The frame is usually transmitted serially and contains a header fieldand a trailer field that “frame” the data. Part of the frame that istransmitted by an 802.11 WLAN device is called the preamble, withdiffering preamble formats for the various protocols. For instance, thepreamble for an 802.11a device comprises ten short and two long symbolsused for synchronization and may contain data pertinent to signaldetection such as Automatic Gain Control (AGC), diversity selection,frequency offset estimation, timing synchronization, etc. It should benoted that the preamble for other 802.11 devices such as 802.11b and802.11g is different from that of an 802.11a device. For instance,802.11b does not include short symbols in the preamble trainingsequence.

In accordance with the present invention, the preamble transmitted byany 802.11 WLAN device has a further use by wireless communicationsdevice 10.

Additionally, the preamble may be used to verify the relative quality ofsignals received by the multiple antennas. In other words, the presentinvention may be applied to all 802.11 protocols including the mostpopular ones, i.e., 802.11b, 802.11a, 802.11g and 802.11n. The preambleas a whole, no matter whether repeating or not, may be subdivided andindividual portions used by the different antennas. Thus, the subdividedpreamble portions for any 802.11 protocol may be used for trainingwireless communications device 10.

The antenna selection scheme illustrates the dynamic selection andantenna priority process that enables wireless communications device 10to process signals having the highest quality. By way of example, thefour antennas A₀, A₁, A₂ and A₃ may be partitioned into two groups, withone group including antennas A₀ and A₂ and the other group includingantennas A₁ and A₃. With the arrival of the first portion of thepreamble, receiver 12 sequentially evaluates the signals received by theantennas in the first group during the training period. By way ofexample, antenna A₀ may use the first 5.5 symbols and antenna A₂ may usethe subsequent 1.8 symbols. Then, with the arrival of the each symbol,receiver 12 sequentially evaluates the signals received from antennas inthe second group during the second short training symbol.

A comparison of the signals received by the first group may show thesignal received by antenna A₀, for example, to be the highest quality. Acomparison of the signals received by the second group may show thesignal received by antenna A₁, for example, to be the highest quality.Then, a further comparison between the highest rated signals andcorresponding antennas from the first and second groups may show, forexample, that the signal received by antenna A₀ to be the highestquality. Accordingly, antenna A₀ may be selected for the “first tiergroup” with the other antennas placed in the “second tier group.”

Thus, in this embodiment channel evaluation circuit 34 (see FIG. 1)evaluates signals received by all of the antennas, selecting the oneantenna that provides the highest quality signal for the “first tiergroup” and holding all other antennas in the “second tier group.” Assubsequent preamble packets are received, switch controller 32 “pairs”the one antenna in the “first tier group” with an antenna selected fromthe “second tier group”. With the arrival of each preamble packet,channel evaluation circuit 34 pairs the one antenna with a differentantenna selected from the “second tier group” to determine the antennacombination that provides wireless communications device 10 with thehighest performance.

By pairing the one antenna from the “first tier group” in sequentialfashion with an antenna selected from the “second tier group”, theantennas and antenna combinations may be evaluated. Based on theevaluations, a determination may be made as to whether the antenna inthe “first tier group” should be replaced with an antenna from the“second tier group” if that antenna provides a higher quality signal. Byway of example, antenna A₀ in position 0 may be exchanged with antennaA₁ in position 1. In this case, antenna A₁ in position 0 is the oneantenna in the “first tier group” that is combined with antenna selectedfrom the “second tier group” for evaluation.

It should be pointed out that the scheme illustrated in FIG. 2 fordynamically tracking the channel variation may be generalized toevaluate more than two antennas for each preambled packet. This may bevery useful for 802.11b that has longer preambles that may be used bywireless communications device 10 to support additional antennaevaluations. One modification from the illustrated scheme may includeselecting M−1 antennas in the second tier group (instead of selectingthe one antenna as shown). With longer preambles receiver 12 is capableof evaluating M antennas for each preambled packet. By way of example,receiver 12 may select antennas at positions mod(i, N−1)+1, . . . ,mod(i+M−1,N−1)+1 for evaluation during the current preambled packet andset i=mod(i+M−1,N−1)+1 for the next preambled packet.

FIG. 3 is a diagram showing the evaluation process for the schemeillustrated in FIG. 2 for selecting two antennas to provide wirelesscommunications device 10 with the highest performance. In this processthe one antenna in position 0 from the “first tier group” is evaluated(Block 210). An antenna from the “second tier group”, i.e., an antennain position 1, 2, 3, . . . , or N−1, is selected for evaluation (Block212). Following the evaluation and comparison of the two antennas, theantenna with the best signal quality is selected and a determinationmade as to whether the packet is detected (Block 214). If the packet isnot detected, the signals from the antenna are evaluated again.

On the other hand, if the packet is detected a determination is madeabout the relative signal quality of the one antenna in position 0 andthe paired antenna from the “second tier group” (Block 216). If theantenna in the “first tier group” has the best signal quality, switchcontroller 32 (see FIG. 1) selects the signal from the antenna in “firsttier group” for processing through receiver 12 in decoding the receivedmessage (Block 218). The address in the packet sent by the AP isverified (Block 220), and if valid, the one antenna in position 0 fromthe “first tier group” is paired with another antenna from the “secondtier group” (Block 228) to start the evaluation process for the nextpacket.

Returning to Block 216, if the antenna in the “first tier group” doesnot have the best signal quality, switch controller 32 (see FIG. 1)selects the signal from the paired antenna in “second tier group” forprocessing through receiver 12 in decoding the received message (Block222). The address in the packet sent by the AP is verified (Block 224),and if valid, the paired antenna from the “second tier group” isexchanged with the antenna from the “first tier group” (Block 226).Again, the antenna providing the highest quality signal is placed inposition 0 in the “first tier group”. The antenna in position 0 ispaired with an antenna from the “second tier group” (Block 228) to startthe evaluation process for the next packet.

The antenna receiving the signal having the highest quality is detectedwithin three packets and that antenna is selected and employed toreceive further packets. Thus, this scheme dynamically determines thebest antenna from all other antennas and directs switch controller 32 toactively receive further packets from that antenna.

FIG. 4 illustrates another embodiment that dynamically tracks channelvariations that may affect the signals received by the multiple antennasin receiver 12. This embodiment includes at least two antennas in the“first tier group”, with antennas being placed in this group based on ahigher probability of receiving quality signals. For the example wherewireless communications device 10 includes four antennas, two antennas(e.g., antennas A₀ and A₂) are placed in the “first tier group” and twoantennas (e.g., antennas A₁ and A₃) are placed in the “second tiergroup”. A comparison “a” between antennas A₀ and A₂ is more frequentthan comparisons “b” or “c” because antennas A₀ and A₂ have beenevaluated as the most likely candidates to provide the highest qualitysignals.

Various comparison sequences are possible. One example is a sequence ofcomparisons a, b, a, c, followed by a repeat of the sequence. Anotherexample is sequence of comparisons a, a, b, a, a, c, followed by arepeat of the sequence. For any comparison sequence, antenna mayexchange groups in order to maintain the “first tier group” as theantennas with the higher probability of receiving quality signals. Thus,after each comparison the antennas may be repositioned to maintainantenna in the proper tier groups.

FIG. 5 illustrates a comparison scheme for yet another embodiment thatdynamically tracks channel variations that may affect the signalsreceived by the multiple antennas in receiver 12. This embodimentincludes more antennas in the “first tier group” than in the “secondtier group.” The antenna partitioning for this embodiment may be suited,for example, a Line-Of-Sight (LOS) situation where one sector has thebest signal and two neighboring sectors have the second/third bestchannels. At least these three antennas would be placed in the “firsttier group” based on a higher probability of receiving quality signals.Antenna for other antenna sectors would be placed in the “second tiergroup.”

Various comparison sequences are again possible. One example is asequence of comparisons a, b, a, b, c, followed by a repeat of thesequence. Another example is sequence of comparisons a, b, a, b, a, b,c, followed by a repeat of the sequence. The comparison sequences areintended to increase the likelihood of choosing the antenna thatprovides the best quality signal. For any comparison sequence, antennamay exchange groups in order to maintain the “first tier group” as theantennas with the higher probability of receiving quality signals. Thus,after each comparison the antennas may be repositioned to maintainantenna in the proper tier groups.

FIG. 6 illustrates a procedure for initiating coverage or booting upwireless communications device 10. Channel evaluation circuit 34 andswitch controller 32 direct switch 36 to rotate or cycle through themultiple antennas until detecting a packet (Block 610). The message isdecoded (Block 620) by processor 24 and checked for a correct addressfrom the AP (Block 630). The antenna that provided the packet is placedin position 0, i.e., indicating the highest priority for receiving aquality signal, and other antenna are placed in other positions (Block640). One of the schemes used to evaluate and compare signals isselected by processor 24 and made operational in wireless communicationsdevice 10 (Block 650).

By now it should be apparent that a method and circuitry have beenpresented for incorporating multiple antenna with one receiver chain andselecting the antenna that provide the highest quality signals to theprocessor. The signal quality may be evaluated using the preamble or thebeacon signals to ensure that the wireless device receives the bestquality signals possible.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those skilled in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method, comprising: partitioning multiple antennas into a firsttier and a second tier, the first tier having one antenna selected as areceiving antenna and non-selected antenna in the second tier; receivinga framed digital signal having preamble symbols in a mobile device;sequentially switching the non-selected antenna in the second tier toprocess portions of the preamble symbols in a receiver of the mobiledevice to evaluate a signal quality of signals received by thenon-selected antenna; and pairing each non-selected antenna in thesecond tier, one by one, with the receiving antenna in the first tier todynamically determine a pair having a highest signal quality.
 2. Themethod of claim 1 wherein evaluating a signal quality of signalsreceived by the non-selected antenna further comprises: demodulating thesignals in a single receiver chain to generate quadrature signals; andcomparing the quadrature signals to determine which of the non-selectedantenna in the second tier provides a higher signal quality.
 3. Themethod of claim 1 further comprising: comparing the signal quality ofthe signals received by the non-selected antenna in the second tier, oneby one, with a signal quality of the receiving antenna in the first tierto dynamically determine an antenna having a higher signal quality. 4.The method of claim 1 further comprising: evaluating each pair todetermine whether to replace the receiving antenna in the first tierwith a non-selected antenna in the second tier.
 5. The method of claim 1further comprising: replacing the receiving antenna in the first tierwith a non-selected antenna in the second tier that has a higher signalquality than the receiving antenna in the first tier.
 6. A method,comprising: partitioning a first antenna in a first tier and second andthird antennas in a second tier; controlling a switch in a transceiverof a mobile device to sequentially provide signals received by thesecond and third antennas to an input of a single receiver wherepreamble symbols are used to evaluate signal quality for the second andthird antennas in a single frame; and pairing the second and thirdantennas in the second tier, one by one, with the first antenna in thefirst tier to dynamically determine a pair having a highest signalquality.
 7. The method of claim 6 further comprising: comparing thesignal quality of the signals received by the second and third antennasin the second tier, one by one, with the signal quality of the firstantenna in the first tier to dynamically determine an antenna having ahigher signal quality.
 8. The method of claim 6 further comprising:selecting the second or third antenna having a higher signal qualitythan a signal quality of the first antenna to replace the first antennain the first tier.
 9. The method of claim 6 further comprising:evaluating the signals received by the second and third antennas tocompare the signals received by the second and third antennas as to thesignal quality.
 10. The method of claim 6 further comprising: evaluatingeach pair to determine whether to replace the first antenna in the firsttier with the second or third antennas in the second tier; and replacingthe first antenna in the first tier with the second or third antennas inthe second tier that has a higher signal quality than the first antennain the first tier.
 11. A system comprising: a Network Interface Card(NIC) having at least three antennas coupled through a switch to aninput of a single receiver in a mobile device; and a processor coupledto the single receiver to compare quadrature signals that aredemodulated from preamble symbols sequentially received by the at leastthree antennas, wherein the processor selects an antenna that provides ahighest quality signal as a receiving antenna in a first tier and placesthe second and third antennas in a second tier, and pairs the second andthird antennas in the second tier, one by one, with the receivingantenna in the first tier to dynamically determine a pair having ahigher signal quality.
 12. The system of claim 11 wherein the processorfurther compares a signal quality of the signals received by the secondand third antennas in the second tier, one by one, with a signal qualityof the receiving antenna in the first tier to dynamically determine anantenna having a higher signal quality.
 13. The system of claim 11wherein the processor further selects the second or third antenna havinga higher signal quality than a signal quality of the receiving antennato replace the receiving antenna in the first tier as the receivingantenna for the mobile device.
 14. The system of claim 11, wherein thepreamble symbol is received from an 802.11 a/b station and the preamblesymbol includes ten short and two long symbols.
 15. The system of claim11 further including: a Static Random Access Memory (SRAM) coupled tothe processor.
 16. An article, comprising: selecting an antenna thatprovides a highest quality signal as a receiving antenna in a first tierand placing non-selected antenna in a second tier; retrieving a frameddigital signal having preamble symbols in a mobile device; pairing eachnon-selected antenna in the second tier, one by one, with the receivingantenna in the first tier where the preamble symbols are used todynamically determine a pair having a highest signal quality.
 17. Thearticle of claim 16 further comprising: comparing a signal quality ofthe signals received by the non-selected antenna in the second tier, oneby one, with a signal quality of the receiving antenna in the first tierto dynamically determine an antenna having a higher signal quality. 18.The article of claim 16 further comprising: selecting a non-selectedantenna having a higher signal quality than a signal quality of thereceiving antenna to replace the receiving antenna in the first tier.19. The article of claim 16 further comprising: evaluating each pair todetermine whether to replace the receiving antenna in the first tierwith a non-selected antenna in the second tier; and replacing thereceiving antenna in the first tier with the non-selected antenna in thesecond tier that has a higher signal quality than the receiving antennain the first tier.